Position or object location systems are finding increasing application in manufacturing and materials handling environments. For example, such systems have utility for factory automation, including such applications as tool automation, process control, robotics, autonomous guided vehicles, computer-integrated-manufacturing (CIM), and just-in-time (JIT) inventory control.
One approach to position location systems uses transmitters, or tags, attached to objects to be tracked, and an array of receivers for receiving tag transmissions throughout a tracking area. Tag transmissions can be effected by radio, ultrasonic or optical communications, using various techniques for identifying object movement or location in the near range of a receiver.
Radio communication provides a high degree of accuracy and performance superior to ultrasonics and optics in terms of: (a) range per watt of power; and (b) penetrability through opaque structures. However, a problem with radio communications in the typical business environment--which includes walls, silvered windows and other fixed structures--is that, for the frequencies of interest (i.e., above 100 MHz), random reflections introduce multipath distortions in tag transmissions arriving at a given receiver. Moreover, in such an environment, the unpredictable attenuation of transmissions passing through walls and other structures makes signal strength only marginally useful for communicating distance/location information.
Accordingly, a need exists for a position location system capable of being used to locate objects in an environment subject to the effects of multipath reflections.